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glibc  2.9
Functions
ldbl2mpn.c File Reference
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
#include <ieee754.h>
#include <float.h>
#include <math.h>
#include <stdlib.h>

Go to the source code of this file.

Functions

mp_size_t __mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size, int *expt, int *is_neg, long double value)

Function Documentation

mp_size_t __mpn_extract_long_double ( mp_ptr  res_ptr,
mp_size_t  size,
int expt,
int is_neg,
long double  value 
)

Definition at line 33 of file ldbl2mpn.c.

{
  union ieee854_long_double u;
  u.d = value;

  *is_neg = u.ieee.negative;
  *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS;

#if BITS_PER_MP_LIMB == 32
  res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction.  */
  res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits.  */
  #define N 2
#elif BITS_PER_MP_LIMB == 64
  /* Hopefully the compiler will combine the two bitfield extracts
     and this composition into just the original quadword extract.  */
  res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
  #define N 1
#else
  #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
#endif

  if (u.ieee.exponent == 0)
    {
      /* A biased exponent of zero is a special case.
        Either it is a zero or it is a denormal number.  */
      if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */
       /* It's zero.  */
       *expt = 0;
      else
       {
          /* It is a denormal number, meaning it has no implicit leading
            one bit, and its exponent is in fact the format minimum.  */
         int cnt;

         if (res_ptr[N - 1] != 0)
           {
             count_leading_zeros (cnt, res_ptr[N - 1]);
             if (cnt != 0)
              {
#if N == 2
                 res_ptr[N - 1] = res_ptr[N - 1] << cnt
                                | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
                 res_ptr[0] <<= cnt;
#else
                 res_ptr[N - 1] <<= cnt;
#endif
              }
             *expt = LDBL_MIN_EXP - 1 - cnt;
           }
         else
           {
             count_leading_zeros (cnt, res_ptr[0]);
             res_ptr[N - 1] = res_ptr[0] << cnt;
             res_ptr[0] = 0;
             *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt;
           }
       }
    }

  return N;
}

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